You can block single sender address (user@domain.com), whole domain (@domain.com), IP address (xx.xx.xx.xx) or CIDR IP range (xx.xx.xx.0/24, etc) this way. But iRedMail will have 3 policies to handle different sender types (single address, whole domain, IP address and CIDR IP range): blacklisted_senders, blacklisted_domains, blacklisted_ips. The reason why we do it this way is for better management in iRedAdmin-Pro, so that admins can easily find/understand different blacklist types.